I had lenovo G500s recently with Windows 8 with 64bit preloaded.I got bored with Windows 8 hence downgraded to Windows 7 Home Premium 64bit.
Windows 7 worked very fine after installing the device drivers except for the LCD brightness that doesn't respond to any fine adjustments.
In the main page of Windows Power Managemet as well as the keyboard hotkeys, the slider either goes to the maximum or minimum brightness (no stages in between though in Windows 8 there were more than 6 stages)
In the advanced settings screen, as far as I adjust brightness (for example to 50% on battery, 70% plugged in) this doesn't lead to any change in the brightness practically.
How to solve this?
A BIOS update is needed to fix this issue.
It seems that this issue may occur in some systems with below spec:
Lenovo G400s\G500s shipped with panel SEC LTN156AT30-L01 (18200896) with BIOS versions less than V1.11.
For G400s\G500s, update BIOS to 1.11 version or above version.
For G400\G500, update BIOS to 1.07 version or above version.